Communication system



` R. H. CAMPBELL Apr'il 21, 1942.

l COMMUNICATION SYS TEM Filed Nv. 4, 1940 n Nl. j

R. -l. CAMPBELL COMMUNIGATION SYSTEM I April 21, 1942.

2 Snes ns-Sheet 2 Filed Nov. 4, -1940 NNN NNN QN@ WW.

, Patented Apr. 21, 1942 Richard H."`Campbell, ,Itacina Wis., assignor to i Webster Electric Company, Racine, Wis., a corporation-of Delaware Application November 4, 1940,Serial No. 364,133

Y 14 claims'. (o1. 17a- 40) il? The present invention relates to` communication systems and more particularly to intercommunicating systems of the loudspeaking type.

Loudspeaking intercommunicating systemsoi the type employing amplifiers andsound transh lating devices capable of performing the dual functions of a microphone and loudspeaker may be dit vided into two classes in so far as the nature of the units atthe stations constituting `the systems is concerned. One class of system comprises one station, ordinarily called a master station,` having an amplifier, a loudspeaker-microphone, and a communication control switch, and .one or more other` stations, which may be called subi-stations, each having a loudspeaker-microphone. The communication control switch at the master station is arranged alternately to connect `the 'loudspeakermicrophohes at the master and substations to the output and input of the amplifier so that communication may be carried on alternately in opposite directions `between the stations. The second class of system comprises two `or more master stations withwhich may be u combined one or more sub-stations.

Insystems of both classes, in sub-stations to `originate a ca ll, it isknecessary that the amplifier at the master station be normally operative, and as a result power ,is `consumed even when the system Ais `not being used. A primary object of the present invention is the ,provision of a communication system wherein the amplifier at a `master station is vmaintained normallyV operative, but with reduced B potential. By supplying the amplier with reduced B potential,` a number of `advantages `are realized. One is that the sub-stations not provided with amplifiers can call themaster stations. A second is thatpower consumptionis reduced duringthose periods when the `apparatus lis not being utilized and the life of the tubesof the amz' pliers is increased. Third,A the squawk resulting from the connection of theoutput of one ampliiier `to the input of another amplienin systems comprising a plurality of master stations is minimized. Y l u `A further object of the present invention is to provide new and improved circuitarrangements embodying normally operativeamplifiers.`

A further object of the presentinvention is to provide a simplied system comprising `a number of master stations and a number of sub-stations, whereby the operator is readily enabledto select either type of station and readily manipulate the communication control switch yin order topro- ,u

order for the Y. t

T155 `system comprising a plurality of master and sub- `stations and rin `which the selection of master vide alternate two-way communication with the particular type of station selected. u t

u Other objects and advantages of the present invention will become apparent from the ensuing description, in the course of `which ,reference4 is had to the accompanying drawings in which:

Fig. 1 is a schematic circuit diagram illusf trating one embodiment 4of the invention, which embodiment comprises a plurality `of master and sub-stations; 1 u

Fig. 2-is a schematic circuit diagram of a systemembodying the invention, which system comprises a single master station and a plurality of sub-stations; i and l l l Fig. 3 isa schematic circuit diagram of another and sub-stations and determination of the proper mode of operationof the communication control switch are simplified. l

`Referring now to Fig. 1, it may be seen that the illustrated system is ofthe` loudspeaking type wherein communication is carried on alternately in opposite directions under the control of manually operable communication direction control switches at the master stations.

The master` stations are indicated by reference characters I and 2, and thesub-stations by ref- `er'ence characters 3, 4 and 5.'v While only a limited number of both types of. stations have been illustrated, it `should be,` understood that the number of stations may be varied to meet the requirements of any particular installation. All the stations are provided with translating devices capable of being utilized vboth asmicrophonesand loudspeakers, such as the devices II to I5, inclusive, which may be of the well-known permanent magnet type. These devices will be referred to hereinafter as loudspeakers. Master `stations I and 2 are provided with amplifiers I6 and Il, manually operable three-position communication `direction control switches I8 and I9, and station selector switches 201and 2l, all respectively. While the station selector switches have been illustrated as being ofthe rotary type, it should be understood that push button switches may be utilized. The 'sub-stations are provided with call switches 22, 23and 24, respectively, so arranged in circuits that calls may be originated at the` sub-'stations and so that the latter may transmit messages to master sta- .tions lbut that the master stations cannot eavesdrop on the sub-stations.

i g The amplifiers may be of any well-known construction, and accordingly they have not `been OFFICE@ V illustrated in detail. The ampliers may be supplied with suitable energizing current, either alternating or direct current, through conductors indicated by reference characters 25. The ampliiiers are normally operative, but the B supply is reduced, thereby to reduce power consumption during standby, to increase the life of the amplifier tubes, and to minimize the squawk resulting from double ainpliiication.

Considering now the apparatus of station I, it may be seen that the B supply circuit indicated by reference character 26 is normally completed through a resistor 21 by the uppermost switch blade 28 of the three-position communication control switch I8.

In the-normal position of switch I8, in which it is shown, the B supply circuit is completed through the resistor 21, as previously described. Loudspeaker II is connected to the output of the amplifier through a circuit including conductors 29, 30, 3|, lowermost switch blade 32 of switch I8, and conductor 33, the return circuit being completed by a common conductor 34 which may be the shield covering interstation conductors, to which reference will .be had shortly. This normal connection of the loudspeaker to the output of the amplifier prevents other stations from eavesdropping on the station. The input of the amplifier is connected to an interstation conductor 4I individual to station I by a circuit including conductor 35, switch blade 36 of switch I8, and conductor 31. Switch I8 also includes a fourth switch blade 38 connected by conductor 39 to selector switch 2D. In the normal position of switch I8 blade 38 does not perform any useful function as conductor 40, with which it is in circuit, as well as conductor 40', which is connected to conductor 40, are disconnected from other circuits.

In addition to interstation conductors 34 and 4I, to which reference has already been made, the system comprises a number of interstation conductors 42, 43, 44 and 45 individual to stations 2, 3, 4 and 5, respectively, However, before describing the remainder of the system, it is deemed best to complete the description of the circuits at station I as well as the operation of communication control switch I8.

The communication control switch is operable to its lowermost position to call a sub-station or to answer a call from another master station. In this position loudspeaker II is connected to the input of the ampliiier, and the output of the amplifier is connected to the selector switch 2|] and .by the latter to the interstation conductor individual to a selected station. At this time resistor 21 is cut out of circuit by switch blade 28 so that the full B potential is supplied to the amplifier tubes and the full output of the amplier utilized. Loudspeaker II is connected to the input of the amplier through a circuit including conductors 29, 38, 3I, switch blade 36, and conductor 35. The output of the amplifier is oonnected to selector switch 20 through a circuit including conductor 33, switch blade 32, conductors 40 and 40', switch blade 38 and conductor 39.

The communication control switch I8 is also operable into a third position, its uppermost position, in order to call another master station. At this time the amplifier is rendered inoperative, by reason of switch blade 28 breaking the B supply circuit and switch blade 32 short-circuiting the amplifier output through a circuit including conductors 33 and 46, and loudspeaker II is connected directly to the selected interstation conductor through a circuit including conductor 29, switch .blade 38, conductor 39, and selector switch 20.

The equipment at station 2 and its mode of operation corresponds substantially to that at station I. The selector switch 2I, however, is normally positioned to complete a circuit from interstation conductor 42, which, it may be remembered, is the conductor individual to station 2, and conductor 42 is furthermore connected by a conductor 41 to a contact associated with a switch blade 36 corresponding to switch blade 36 at station I. In view of the identical nature between the apparatus at stations I and 2, except as noted immediately above, it is deemed unnecessary further to elaborate upon the description of the equipment at this station.

Loudspeakers I3, I4 and I5 at stations 3, 4 and 5 are connected by conductors 48, 43 and 58 to interstation conductors 43, 44 and 45 respectively. The loudspeakers are also connected to common conductor 34. The call switches 22, 23 and 24 are connected directly to conductors 48, 49 and 50 and are operable to connect their associated loudspeakers to either of conductors 5I and 52, which are connected, respectively, to conductors 4I and 42 individual to stations I and 2.

In the description of the operation of the systern of Fig, 1, it is assumed that the amplifiers I6 and I1 are supplied with suitable energizing current and that the communication control switches I8 and I9 are in their illustrated positions, so that the ampliers are normally operative with reduced B potential. Assuming rst that an operator at station 2 desires to communicate with the operator at station I, then it is necessary for the operator at station 2 rst to select station I by moving selector switch 2| to complete a circuit to interstation conductor 4I, and then to manipulate the communication control switch I9 to its uppermost position. This results in the connection of loudspeaker I2 to the input of amplifier I6 through a circuit including a blade of communication control switch I9, selector lswitch 2|, conductor 4I, selector switch 28, conductor 31, switch blade 35, and conductor 35, the input circuit being completed through the common conductor 34. Loudspeaker II at station I is connected to the output of amplifier I6, and as a consequence, the operator at station 2 may call the operator at station I. Thereafter, the operator at station I controls the direction of communication by operation of the communication control switch I8 at station I from its indicated to its lowermost position, thereby alternately to connect the loudspeakers I I and I2 to the output and input of amplier I6. When the call is completed, the selector and communication control switches are returned to their indicated positions. If desired, the latter may be provided with springs 58 operable to return them to their indicated positions from their lowermost positions.

When the operator at station I desires to call the operator at station 2, the above described procedure need only to be reversed.

The mode of communication 4between a master station anda sub-station will be described in connection with stations I and 3. If the operator at station I desires to call station 3, the selectorl switch 20 is first operated to complete a circuit to interstation conductor 43, and communication control switch I8 is then operated to its lowermost position, thereby to connect loudspeaker II to the input of amplifier IE and loudspeaker i la tof tnecutput ofthe ampii'aer.` To

respond, the operator at the substation"operates switch 22 to complete a circuit from loudspeaker AI3 to conductor `4I through conductor l 5I ,l after whiclrthe operator atthefmasterstation controls ther direction offcommunication, *as previously tocfonductorjl". @With selector switch 2ll`fan`d communication control `switch `I8"in their indicatedpositions,"loudspeaker I3 is connected' to the iriput of theainplifierthrough a, circuit in`- v and conductor 35, thecirouit being completed throug'hfthe'common,conductor 34. `Upon receipt o ffthe'call;` the operator at station I vpref,-

conductor "I9, switch"y bladeflfand conductor 82. In its `intermediate position, the communication control, switch 64V is effective to cut out resistor "14; thereby to supply full B potential to the amplifier while maintaining unchanged the circuitconnections to the input `and output of the amplifier."`As a result, incoming calls may. be heard at full volume. `In'the lowermost position of communication controlswitch 64, loudspeaker II` is connected lto the'- input of the amplifier throughv a circuit includingconductors IB and 82 and `switch blade 16,1while the selector switch is connectedto theoutput of lthe amplifier through a circuit including conductors 'I9 'and III]` and switch made `141. f

` When the communication control and "selector switches 64 and 65fare inttheirindicated posi-` tions,fcalls may bel originated at the substations erably movesselectorswitch to completea cirl cuitto conductor 43 and thereaftercornmunica- -tionis 'carried on in alternatedirections by op-` eration ofswitch Ifat station I between its indicated andflowermost` positions. When ay call is originated by a sub-station, it is not necessary that the'selector switchat the called master station-be operated; as*two-wayfcommunication can bei.v carried on over the` circuit individual to the master station. s

From the foregoing description of the embodiment of the invention illustrated inFig. 1`, it may befseen that powerconsumption `is reduced during stand-by periods, that is, when the apparatusf is not being utilized, and the life of the tubes is increased by reason of the fact that a reduced B? `potential is utilized. Furthermore, if the output of one ofi theampliers is `inadvertently connected to the input of theother,` the squawk resulting from this double amplification is minimized` i In addition, sub-stations not'provided with amplifiers can call master stations but masterstations cannot eavesdropV on sub-stations as the loudspeakers atlthe sub-stations cannot be connected to Y the inputs yof the amplifiers unle'ss thejswitches 22, etc., thereat areioperated.

`InFig. 2` the'invention is illustrated in connec; tion with a system comprisingafsingle master station and a `plurality of sub-stations. The

master station, indicated by `reference character I', is provided witha normally 'operative amplier 62,` a loudspeaker II ,a communication control switch 64, and aiselector `switch 65. fIhefsubstations, indicated by reference characters 3 and 4, are provided withloudspeakers I3, I4, and call switches 'I0 and 1I, respectively. The amplifier is supplied withA suitable-power through conductors 12, and when thecommunication control switch 641s in `its indicated position, the B supply circuit for the` amplifier" is completed through conductors y'I3,.resistor 14, and the upperrnost switch blade 15of switch 64.

The communication' `control switch includes also switch blades `S16 and I1,` thefformer of which is connected by conductor `18 to'loudspeaker II and the latter of which is connected ,bylconductor 'I9 to` selector switch 65. L In the indicated position of switch 64, loudspeaker II is i connected to the output of amplifier 62 through put `of the 4arnplifierzthrough a circuit'including byoperation of thecallswitches 10 or 1I. In its indicatedV position, selector switch 65` completes a^^circuit3 to interstation conductor 83 so that upon-closure of switches' I0 or 1I, loudspeaker I3 orf I4 is connected tothe input of the amplifier 62through 1a` previously described circuit. Upon res'pimdingtothe call,.the` operator at station I 'manipul'atesl selector switch `65 toV complete a circuit lto thecallingsub-station through either conductor 84 or conductor 85,."which"conductors are respectivelyassociated'with `stations 3 and 4.

Reviewing'the operationof the system of Fig. 2,v it may be `seen'that themaster station may call either sub-station by operation of selector switch 65to s'electthe` desired sub-station, and thereafter :opera'tingV communication control switch 64 to its lowermostposition. At this time,

as previously described, loudspeaker II is connectedtothe `input of amplifier 62 and the output of `the latter islconnected to the selected sub-statior'i through the switch `blade 11', conduc`" tor 19,an'd selector` switch lili. Communication may thereafter be carriedl on iniopposite directions by operationA of `communication control switch 64 alternately to itslowermost and intermediate positions.` This communication is at full Volume as the resistor `14` is not inserted in the `Bf supply circuit. `Upon completion of the call, thecommunication lcontrol and selector switches are returned to their YindicatedV positions.

Incase `the operator at one of the sub-stations,

sub-station 3 for instance,` desires to callzthe operator at the master station,` itis necessary only for theformer to close `switch 10. ,This results in the connection of'loudspeakerrI3 to the input of 'the `amplifier through a circuit including conductor` 83 selector switch 65, conductor 19,

switch blade 11, and conductor 82.` Inasmuch `as loudspeaker I'I is connectedlto the output of amplifier i62,1 the operator at the master station is enabled to receiv'ethe call, after which communicationmay be carriedwon between the two stationsV `aswthough the call originated at the masterxstation.

`The systemof Fig.` `3 combines the normally operative amplifier with a jselector switch arrangement enabling the operators atmaster stations readily to call either other master stations or sub-stations, and at the same time enabling thejoperators readily-to determine the proper mode fof manipulation of the communication control `switches for. the selected type of station.

Referring now to Fig.V 3s, it may be seen that like the embodiment of Fig. 1, the system comprisesltwo master stations, indicated'by reference characters I and 2,' and three sub-stations, indicated'by reference characters,3',u4 and 5, and

that :these stations 'are provided with loudspeakerslrl Ito: `|5,:in::lusiv,e. -The master stations: are

providedawithf:amplifiers I6 and communication vcontrol, switchesA 9|,'92," and with a first set of selector switches 93 and 94 for selecting sub stationsand asecond set ofselector switches 95 and 9S. for selecting the master stations. The amplifiers are supplied-with suitable energizing power through conductors 91.

The mode of operation of the communication control switchesatthe master stationsy is dependentupon whether a sub-station or another master station is selected. When a master station is selected the communication control switch is operated from its intermediate position, Ain which it yis'shown, to its lowermost position. In this position, the loudspeaker at the master station is connected to the output of the amplifier of another station for receptiomand` in the lowermost position, the loudspeaker is connected to the input of the amplifier at that station for transmission. When a sub-station is selected, the

communication control switch is operated between its uppermost andv lowermost positions. In the uppermost position, the loudspeaker atthe sub-station is connected to the input ofthe amplifier and the -output ofthe amplifier is connected to the loudspeaker at the master station. In the lowermost position, the connectionsof the two loudspeakers to the amplifier are reversed.

Referring again to Fig. 3, it may be seen that the communication-control switch 9| at station comprises four switch blades, |02, |03 and |04. Blade |0| is adapted inthe indicated position of the switch to break the B supply circuit which extends to the switch blade through conductors |05, thereby rendering the amplifier inoperative. In the uppermost position of switch 9|, a reduced.B-l potential is suppliedy tothe amplifier through resistor |06, and in the lowermost position, the full B potential is supplied to the amplifier, the resistor |06 being cut out ofcircuitand the B supply circuit being completed throughconductors and switch blade |0-|. Switch blade |02 is connected by conductor -|0'|' to loudspeaker V| and in the indicated position of' switch 9|f,f.the loudspeaker is connected to an interstation conductor |08- individual tov vstation for the reception of calls from other master stations.A Switch blade |03 is connected by conductor |09 to the substation selector switch' 93. The selector switch 93 comprises a number of individual switches equal to the number of sub-stations-three in this` case. The sub-stations are connected to interstation conductors ||0, and ||3 individual thereto. Switch blade |04 is connected by conductors ||4 and |I5 to the output of the amplifier. The input ofthe ampliiier is connected by conductor ||6to the lowermost fixed contact associated with switch blade |02 and to the uppermost fixed contact associated with switch blade |03. One terminal of each ofthe amplifier input and output connections as well as of the various loudspeakers is connected to a common conductor The master station selector switch 95 is also shown to consist Vof a number of individual switches one less than the number of master stations 'in the system. These switches ar-e connected by conductor ||8 to the lowermost fixed contact associated with switch blade |04. The individual switches of selector switch 95 are adapted to connect conductor ||8 to a conductor 9 individual"tostationv 2 and to conductors |20 and l2 |l individual to other master stations of the system, which stations, however, have not been illustrated.

The apparatus and equipment at station 2 correspond identically with that of station with exception of the fact that the switch blade |02 correspondingA to switch blade |02 at station is connected to conductor ||9, the conductor individual to station 2. l.

Communication control switches A9| and 92 have two normal positions. 1 One normal position is the position indicated, at which time the master stationsl are conditioned for reception of calls from other master stationsggand the other normal position is the uppermostposition, at which time the amplifier is rendered operative with a reduced B potential for the reception of calls from'the sub-stations through the closed selector switches 93.

The operation of the system will first be described with the master stationsv conditioned for reception of calls from other-master stations, at which time the communication control switches 9| and 92A occupy the indicated positions. In the event station desiresto communicate with station 2, a selector switch is'operated-to connect conductor 8 to conductor I 9, and the communication control switch 9| -operated to its lowermost position, thereby to render operative the amplifier I6 and to connect'loudspeaker to the input of amplier I6, and to connect the output of the amplifier to conductor ||9 which is connected to loudspeaker |2 at station 2. In answering, the operator at station 2 first closes the uppermost selector switch, which is associated with conductor |08, and then operates communication control switch 92 to its lowermost position To listen to the answerof the operator at station 2, the communication` control switch at station |,is returned to its indicated position. Thereafter, communication in alternate directions is accomplished by alternate operation of the communication control switches at stations and 2 to their intermediate and lowermost positions.

In order to condition the system for reception of calls from the sub-stations, the communication control switches 93 or 94 are closed and the communication control switchesV 9| or 92 operated to their uppermost positions. When this is done, for instance at station the amplifier is rendered operative with reduced B potential and loudspeaker is connected to the output of the ampliiier for reception of messages from the sub-stationsv which are connected to the input of the amplifier. Loudspeaker is connected to the output of the amplifier through conductor |01, switch blade |02, and conductor 5. 'Ihe loudspeakers at the sub-stations are connected to the input of the amplier through the selector switches 93, vconductor |09, 'switch blade |03, and conductor ||6. Upon reception of a call, the operator at station may return the call by operating the communication control switch to its lowermost position, at which time loudspeaker is connected to the input of amplifier I6, and the output of the amplifier is connected to the calling sub-station through conductors ||5 and ||4, switch blade |03, conductor |09, and the selector switch 93 associated with the calling substation.

From the foregoing it may be noted that the communication control switches at the master stations have two modes of operation and that the mode of operation is dependent upon whether or not `the ycommunication is between master stations` ora master station and a sub-station. By utilization of two sets of. selector switches, one associated with each type of station, the operator at any master station can readily determine the proper mode of operation. Thus, confusion as to the propermode of operation of the communication control switches is avoided. v a

It isftobenoted that while only a comparativelyfew stations have `been shown in each of i the embodiments of the invention illustrated, it should be understood thatthe number of `stations may-be multiplied to any` extent` desired. Furthermore, whileall of the stations illustrated are of the type employing a common conductor, it should be understood that the common conductor may beeliminated and that pairs of conductors may be utilized for each station, in which event thefvarious switches Would be modified accordingly. a

While the invention has been disclosed in connection with specific details of preferredyembodiments thereof, it should be understood that such, details are not intended to be limitativeof the invention except in so far asset forth in the accompanyingy claims. a

`I-Iaving thus i described claim as new and desired `to secure` by Letters Patent of the UnitedStates is: a Y 1. A unitfor useat a station in an intercommunicating lsystem of the loudspeaking type, including in combination, an amplifier, a voicere- `producer, `and means for connecting said voice reproducer tothe output-of `said amplifier and for rendering said amplifier operative with reduced B potential.

, `2. A uniti for use at astation in anintercommunicating system, includingiin combination, an

amplifier, a source of primary power and a source of fB potential for said amplier,a voicereproducer, B potential reducing means, and

a switch meansj for connecting; saidvoice reproducer tothe output of said amplifier and; for rendering effective said B'potential reducing means. i 'i 3. In an intercommunicating `system 4of; the

loudspeaking type, the combination including, an amplier having input andoutput connections,

Aa source of primary power and a` source offB,

potential for, said amplier, a Aloudspeakermicrophone located in` proximity to said amplifier, a loudspeaker-microphone located remote .from said amplifier, \B potential reducing means, and `means including a manually operable switchv and circuits associated with said ampliier,fB potential reducing `means and loudspeaker-microphones controlled by said `switch for `connecting .the first of said loud.- speaker-microphones to the output and the second of said loudspeaker-microphones to the `input of the amplifier andrendering effective ,said `B potential reducing means.

.LIn an intercommunicating system as set `iorthin claim 3, wherein the switch and` circuits are so arranged that in another position of' the switch; the connections. of the loudspeakermicrophones to the amplifier are `reversed and full B potential is supplied tothe amplifier.

5. In an intercommunicating system of the `loudspeaking type, the combination including, a

first station having a normally operative amplifier, a multi-position vcommunication, control switch, a loudspeaker-microphone and amplifier ,B potential reducing means, a second station having a loudspeaker-microphone, and circuits associated Vwith said amplifier,` loudspeaker-mimy invention, what I crophones and B potential reducing means so constructed and arranged with respect to said control switch that in one position of the latter the loudspeaker-microphones at the first and second stations are connected to input and output of the amplifier and the B potential reducing means is rendered effective and that in another position the connections of the loudspeaker-'microphones to the amplifier are reversed and full B potential is supplied to the amplifier. 6. In an intercommunicating system of the loudspeaking type, the combination including, a first station having a normally operative amplifier, a multi-position communication control v switch, a loudspeaker-microphone and amplifier B potential reducing means, a second station having a loudspeaker-microphone, and circuits associated with said amplifier, loudspeaker-,microphones and `B potential reducing means so constructed and arranged with respect to said control switch that in one position of the latter the loudspeaker-microphones at 'the `first and second stations are connected to output and input of the amplifier and the B potential vreducing means is rendered effective andV that in speaker-microphone, an amplifier, a source oi primary power` normally connected to said amplifier, a source of B potential, B potential reducing means and a communication control switch, interstationfcircuits between said `staftions, and means including the control switch at each station and circuits controlled thereby for connecting an interstation circuit to the input of said amplifier, the loudspeaker-microphone to the output of the amplifier and for rendering effective said B potentialreducing means.

v'8. In an intercommunicating system of the vloudspe'aking type, the combination including, a

plurality of stations each having a loudspeakermicrophone, anamplifier, a sourceof primary power normally connected to said amplifier,` a source offB potential, B` potential reducing means," a communication control switch and a station `selector switch, and a number of communication circuits equal to the number of 4stations, the communication control 'switches at each station controlling circuits associated with theA amplifier, B potential reducing means, loudspeaker-,microphone and` selector switch so that in lone position of the communication controlswitch and with the selector switch connected to` aninterstation circuitindividual to the station, that interstation circuit is connected` to the amplifier input by said communication control switch, thefB potential reducing meansis leffective and the loudspeaker-microphone is `connected vto the output of the amplifier, whereby the station is conditioned for reception at reduced volume, and so that in" another position the loudspeaker-microphone is connected to the output of the amplifier, the interstation circuit is connected to theinput of the amplifier through said selector switch and the B potential reducing means is rendered ineffective, whereby V.the

station is conditioned for transmission at full volume.

9. In an intercommunicating system of the loudspeaking type, the combination including, a plurality of stations each having a loudspeakermicrophone, an amplifier, a source of primary power normally connected to said amplifier, a source of B potential, B potential reducing means, acommunication control switch and a station selector switch, and a number of communication circuits equal to the number of stations, the communication control switches at each station controlling circuits associated with the amplifier, B potential reducing means, loudspeaker-microphone and selector' switch so that in` one position of the communication control switch and withY the selector switch connected to an interstation circuit individual tothe station,

that interstation circuit is connected to the ampliiier input by said communication control switch, the B potential reducingV means is effective and the loudspeaker-microphone is connected to the output of the ampliiier, whereby the `station'is conditioned for reception at reduced Volume, and so that in a second position the loudspeaker-microphone is connected to the output of the amplifier, the interstation circuit is connected to the input of the amplier through said Selector switch and the B potential vreducing means is rendered ineffective, whereby the station is conditioned for transmission at full volume, and so that in a third position the amplifier is rendered inoperative by cutting oi its B supply and the loudspeaker-microphone is connected to the selector switch, whereby a selected station connected to said amplier, a source of Bpo'- te'ntial, B potential reducing means, a communication control switch and' a stationlselector switch, a plurality of other stations provided with loudspeaker-microphones and call switches, and

a number of communication circuits equal tothe number of stations, the communication control 'switch at said'rst station controlling circuits aS- sociate'd with the amplifier, B potential reducing means,'loudspeaker-microphone and selector switch so that in one position of the commun'ica'- tion control switch and with the selectorY switch connected to an interstation circuit individual to the station, that interstation circuit isconnected to the ampliiier input by said communication control switch, the B potential reducing means is effective and the loudspeaker-microphone is connected to the output ofthe amplifier, whereby the station is conditioned for reception at reduced volume from said other stations upon operation of the call Vswitches thereat to connect the loudspeaker-microphones to the circuit individual said first station, and so that 'in 'anotherv position the loudspeaker-microphone is connected to the output of vthe amplier, the interstation circuit is 'connected to' the' input of the amplifier through said selector switchand the B potential reducing means is renderedineffective, whereby'the 'station is 'conditioned for transmission to a selected otherst'ation. I i

11. In 'an inte'rcommunicatin'g 'system lof v'the loudspeaking vtypethe combination including, a plurality of stations of the type having a loudspeaker-microphone, amplier, station selecting means and acommunication control switch, a plurality of other 'stations of the type having a loudspeaker-microphone, and interstation circuits between said stations, said communication control switches being operable according to one mode when communication is carried on with a station of the first type and according to another mode when communication is carried on with a station of the other type, and each of said stations of the rst type having separate station selecting means for each type of station to assist the operators thereat in properly operating the communication control switch.

12. In an intercommunicating system of the loudspeaking type, the combination including, a plurality of stations each having a loudspeakermicrophone, an ampliiier, a switch controlling the direction of communication and the B" supply to the amplifier, and two groups of station selector switches, a plurality of other stations each having a loudspeaker-microphone, one of said groups of selector switches being associated with said first mentioned stations and the other with said other stations, interstation circuits between said stations, said communication control switch being so constructed and arranged incircuit with the loudspeaker-microphone, amplifier, B supplycontrolling means, and groups of selector switches, so that when one of said first Amentioned stations is selected the communication control switches at the stations are alternately operable between two positions for reception and transmission, the transmission being through the amplier at the transmitting station, and so that when one of said other stations is selected the "communication control switch at the selecting '40 station is alternately operable between one of rsaid two and a third position for reception and transmission through the amplifier at the selecting station.

13. In an intercommunicating system-of the loudspeaking type, the combination including, a plurality of master stations each having a loudspeaker-microphone, an amplifier, a switch controlling the direction of communication `and also loperable to supply full or reduced B potential Yto or cut 01T the B supply to the amplier, and

Ytwo groups of station selector switches, a plurality of sub-stations each having a loudspeakermicrophone, one of said groups of selector switches being operable to select master stations and the other to select sub-stations, interstation circuits between said stations each of which is individual to a station, the communication control switch yat each station being so constructed and arranged in circuit with the loudspeaker-microphone, amplifier, B supply controlling means, selector switches and interstation circuits that in one position the loudspeaker-microphone is is connected to theinterstation .circuit individual 'thereto andthe ampli'er B" supply is cut off,

i @usr Avenant-u corr plifier and the selector switches associated with the sub-stations are connected to the input of the amplifier, whereby the master station is conditioned for reception from sub-stations.

14. In an intercommunicating system of the loudspeaking type, the combination including, a pair of stations each provided with an amplier, a source of primary power to which the amplier is normally connected, amplifier B potential reducing means, a loudspeaker microphone, a communication control switch and station selector switch means, and interstation circuits between said stations, the communication control switch at eachstation being constructed and arranged with respect to the amplier, B potential reducing means, loudspeaker-microphone and selector switch means so that in a normal position the amplifier is supplied with reducedY B`potential, an interstation circuit is connectedv v nected to the loudspeaker-microphone, and the n amplifier is supplied with full B potential, and

`so that in a third position the amplifier B supply is cut offand the loudspeaker-microphone connected to an interstation circuit, whereby one station can call another by operating the communication control switch thereat toits third position, after which the called station can control the direction of comrrglnication by operation the communication control switch thereat between its first and second positions.

RICHARD H. CAMPBELL. 

